1. Field of the Invention
The present invention relates to a mobile machine for tamping ballast under ties of a railroad track, which comprises a machine frame and spaced undercarriages supporting the machine frame for mobility on the railroad track in an operating direction. The ballast tamping machine has a ballast tamping assembly comprising a vertically adjustable tamping tool carrier, a drive for vertically adjusting the tamping tool carrier, pairs of vibratory and reciprocatory tamping tools immersible in the ballast upon vertical adjustment of the tamping tool carrier, and drives for vibrating and reciprocating the tamping tools.
2. Description of the Prior Art
The ties of a railroad track consisting of two rails fastened to the ties must rest on a well tamped ballast support so that the track retains its desired level and line whereby the quality and the life of the track is enhanced and extended. For this purpose, mobile track tampers of the above-indicated type are used to tamp the ties with tamping tools immersed in the ballast at each longitudinal side of the tie to the left and the right of each rail while the tamper advances intermittently from tamping stage to tamping stage or, in a more recent development of the art, continuously. Preferably, the track is leveled and lined at the same time so that the ties are tamped when the track is in a desired position. U.S. Pat. No. 4,534,295, dated Aug. 13, 1985, discloses a track tamping, leveling and lining operating unit incorporating such a ballast tamping assembly and a track leveling and lining assembly, which comprises a common carrier frame supporting the assemblies, a rear end of the carrier frame being supported on flanged wheels on the railroad track while a front end is linked to a track working machine. However, many types of smaller ballast tamping machines without leveling and lining tools and reference systems are known for minor track rehabilitation work. One such machine having ballast tamping assemblies of the above-indicated type associated with each rail has been disclosed in U.S. Pat. No. 4,476,786, dated Oct. 16, 1984.
Particularly when tamping branch tracks or railroad tracks other than main lines, some ties are obliquely positioned with respect to the rails or are entirely detached therefrom, the rail fastening elements having become loose due to the repeated vibrations to which passing trains subject the track and particularly because the tie wood has rotted, and sometimes because of uneven ballast tamping. Because of the non-uniform spacing of such ties and their lack of parallel alignment with respect to the adjacent ties, it takes longer to tamp these ties individually, and various auxiliary devices, such as tie transport and alignment machines and rail fastening machines, are needed unless the entire track is rehabilitated. In such a general track rehabilitation, damaged ties are exchanged for new ties with special tie exchange apparatus to maintain branch tracks in railroad stations, for example. Such rehabilitation work has to be completed by tamping the replaced ties and then leveling and lining the track with a leveling, lining and tamping machine. Such a replacement of damaged ties is required particularly where spikes are used for fastening the rails to the ties, the indicated problems being aggravated by the fact that rail spikes tend to become loose more readily.
U.S. Pat. No. 4,165,694, dated Aug. 28, 1979, discloses a mobile track leveling, lining and tamping machine which is preceded by a ballast plow arranged to move ballast from the shoulders into the cribs so that there will be sufficient ballast available for the succeeding tamping tools to tamp under the ties whereby a high-quality ballast support is provided for the corrected track. Whether large or small tampers are used and whether the tampers have a relatively high or low efficiency and accuracy, ballast plows have often been used in conjunction therewith, in many instances on independent, self-propelled vehicles. With smaller tamping machines, it is often uneconomical to use relatively large and expensive independent ballast plow machines.
During track rehabilitation work including tie tamping, it has been common practice to replace damaged or mispositioned ties, whose spikes have become loose, by withdrawing such ties from the track and inserting new and properly positioned ties. In copending U.S. application Ser. No. 165,510, filed Mar. 8, 1988, it has been proposed to equip a mobile ballast tamping machine of the first indicated type with a vertically adjustable device associated with the ballast tamping assembly for gripping and transversely positioning a respective tie. This device includes a drive for vertically adjusting the device.